how to access hardware like gpio, i2c in beagle board , running android

Hi Madhu,

You may refer to Android NDK sample applications (hello-jni example) for preparing a jni library.

Thanks,

Pankaj Bharadiya

The Hello-jni is a great example, but there are still issues with permissions.

I have expanded the hello example with code that should activate gpio pin 101 for output.

From an ADB shell I can execute:

    echo 101 > /sys/class/gpio/export

    echo out > /sys/class/gpio/gpio101/direction

    I can then change the output with          echo 1 (or 0) > /sys/class/gpio/gpio101/value

I tried moving this to some JNI code:

 .        eHandle= fopen("/sys/class/gpio/export", "wb");
        r= fwrite("101", 1, 3, eHandle);
         fHandle= fopen("//sys//class/gpio//gpio101//direction", "wb");
        fwrite("out", 1, 3, fHandle);

But this does not get pass the first step of accessing the 'export".

Is this a permissions issue that needs to be addressed in init.rc? Suggestions on how to proceed to control GPIO from JNI?

Thanks

George

Try adding

chmod 755 /sys/class/gpio/export

(or chmod -R 755 /sys )

into the startup script to make all necessary system files accessible from your C code (Android apps don't run with root privileges).

hi, 

i am trying the to toggle GPIO pin using JNI wia  cerating a lib*.so in android-ndk  .and using it in .apk

and in that case i am able to toggle gpio pins using "/sys/class/gpio/*/value" , i also  tried  by direct acesing gpio registers from "/dev/mem" .  and both things are working fine when i am genrating an executable frin android-ndk and runnig on shell.

but the same doesn't work while using form  .apk.

Hi

place your lib*.so in path:/system/lib in your android rootfs.This will make your apk work on your target.

can you share how you toggle that using jni???

Madhu;

There are some security restrictions between layers, you can find some information in next 2 posts, but mostly http://source.android.com/tech/security/index.html

http://e2e.ti.com/support/omap/f/849/p/178679/645155.aspx#645155

http://e2e.ti.com/support/omap/f/849/p/178679/648158.aspx#648158

About platform library read next post,

http://e2e.ti.com/support/embedded/android/f/509/p/190609/684748.aspx

Remember to add required permission at .apk and .jar or .so, used user affects too.

One idea is, you could try to use a platform library to add the permissions (.xml->/system/etc/permissions + <uses-library android:name= in your .apk manifest + ./apk permissions) and register classes to check if it works ok.

Hi Madhu, I've opened a thread with a similar problem that you faced on http://e2e.ti.com/support/embedded/android/f/509/t/346232.aspx

Can you please share your apk and source code so that we may learn too ? It would really help us a great deal.